1. Field of the Invention
The present invention relates to alternating current (AC) power transformers and more particularly to multi-phase AC power transformers for converting one or more input power phases to multi-phase output by selectively configuring windings on a common transformer core structure. Transformers of the present invention are suitable for powering an AC motor variable frequency drive (VFD).
2. Description of the Prior Art
Some known AC variable frequency drives require 9 input current power phases in order to provide drive control to a three phase AC motor. As is shown in FIGS. 1 and 2, each of three power input phases is split to three separate secondaries by known 3-9 phase transformer T. In transformer T, three known paired primary/secondary winding bundles T1, T2, T3 respectively have a primary winding coupled to one of the input power phases over which are wound separate torroidal secondary windings in a so-called delta configuration. In each bundle the primary winding is wound about a separate rung of a commonly shared planar ladder-shaped ferromagnetic laminated core C, and in turn the secondary windings of the bundle are wrapped around the primary winding. Each separate primary/secondary winding bundle T1-3 respectively converts a single phase Φ1, Φ2 Φ3 of three phase AC input power into nine secondaries of output power, collectively ΦA-ΦI. The collective transformer output power ΦA-ΦI are fed to known variable frequency drive VFD, the output power of which controls operational drive parameters of MOTOR.
Thus in known VFD systems ladder core multi-phase transformers require relatively complex internal winding structures in their primary/secondary cores and occupy a relatively large installation footprint.
Known ladder-type core multi-phase transformers generally require ferromagnetic cores specifically configured for a particular phase conversion application. For example, a single phase input, transformer core (often 1 or 2 ladder rung core) has a different structure than one for two phase input (at least 2 ladder rung core) or one for a three phase input (at least 3 ladder rung core). Similarly, multiple configurations of primary/secondary winding bundles are needed depending upon the number of output phases. Bundle manufacture is further complicated because they are not pre-assembled. The bundle primary winding must be wrapped around the ferromagnetic core before the secondary windings can be wrapped around the primary winding. Thus known ladder core transformers require complex core winding configurations and winding procedures that consume large quantities of conductive winding wire.
Thus, a need exists in the art for a modular transformer core structure that can be utilized for multiple types of transformer applications, from single phase input-to-single phase output, single phase input-to-multi-phase output and poly-phase input-to-polyphase output.
Another need exists in the art for a modular transformer winding structure that can be utilized for multiple types of transformer applications, from single phase input-to-single phase output, single phase input-to-multi-phase output and poly-phase input-to-polyphase output.
Yet another need exists in the art for a reconfigurable modular poly-phase transformer that can replace known transformers that are configured for dedicated applications of single input phase-to-multi-output or polyphase input-to-polyphase output, including those commonly using three-phase utility grid line bower for in turn powering polyphase variable frequency drives.
An additional need exists in the art for transformer winding configurations that reduce quantities of conductive winding wire needed for their construction and/or simplify transformer manufacture.